Ultra-thin speakers roll out like wallpaper for sound-blasting surfaces
Engineers at MIT have developed an ultra-thin speaker that could be used to make entire surfaces produce sound. The unique design should be energy efficient and easy to produce at scale, the team says.
In a basic sense, speakers work by vibrating a membrane, which manipulates the air above it to produce sound waves. In speakers commonly found in audio systems or headphones, that’s done using electrical currents and magnetic fields.
But in recent years scientists have developed ways to achieve similar results in much slimmer devices. Thin film speakers work using piezoelectric materials, which vibrate in response to the application of a voltage. These have been used in phones and TVs, and even experimentally to create speakers out of things as unusual as flags.
The problem is, these thin speakers need to either be free-standing or have some separation from another surface – mounting them reduces their ability to vibrate and produce sound. But in the new study, the MIT researchers redesigned thin speakers so they could be mounted on various surfaces.
Instead of having the whole surface of the membrane vibrate, the team formed the material into a grid of raised domes, which vibrate independently of each other. This is done by sandwiching a thin layer of a piezoelectric material, just 8 micrometers thick, between two layers of PET plastic. One PET layer has a grid of tiny holes, through which the piezoelectric material protrudes. The lower PET layer protects the membrane and allows the speaker to be mounted to a surface.
“This is a very simple, straightforward process,” said Jinchi Han, lead author of the study. “It would allow us to produce these loudspeakers in a high-throughput fashion if we integrate it with a roll-to-roll process in the future. That means it could be fabricated in large amounts, like wallpaper to cover walls, cars, or aircraft interiors.”
The resulting speaker measures just 120 microns (0.12 mm) thick and weighs only 2 g (0.07 oz), with thousands of tiny domes measuring 15 micrometers high. To test the device, the researchers mounted it to a wall and measured its output with a microphone 30 cm (11.8 in) away. The speaker was able to produce sound at up to 66 decibels (dB) with 25 V of electricity at 1 kHz, and 86 dB at 10 kHz. The device is energy efficient too, using just 100 milliwatts of power per square meter of speaker.
Along with mountable thin-film speakers, the team says the device could be used as ultrasound detectors, or if covered with a reflective material, to produce unique light displays.
The team demonstrates the speakers in the video below. The research was published in the journal IEEE Transactions of Industrial Electronics.